Lessons 15 · 1 lessons · P. Habibullayev, A. Boydedayev, A. Bahromov, K. Suyarov, J. Usarov, M. Yuldasheva. Physics Grade 9, revised and expanded 3rd edition. G‘afur G‘ulom Publishing House, Tashkent, 2019
15
Chapter I review: tests and summary
Textbook: pp. 44–49
GoalSummarise the main concepts and formulas of Chapter I; prepare for test and calculation tasks.
New words
isoprocesses · izojarayonlarAvogadro constant · Avogadro doimiysiequation of state · holat tenglamasiroot-mean-square speed · o‘rtacha kvadratik tezlik
Explanation
The basis of the chapter is MKT: matter consists of particles that move randomly and interact (Brownian motion and diffusion are evidence). Quantities: ν = N/N_A = m/M, N_A = 6.02·10²³ mol⁻¹, M = m₀N_A, n = N/V. Ideal gas: p = (1/3)nm₀v² = (2/3)nE_k; E_k = (3/2)kT; p = nkT; v = √(3RT/M); R = kN_A = 8.31 J/(mol·K); T = t + 273. Equation of state pV = (m/M)RT, and for constant mass p₁V₁/T₁ = p₂V₂/T₂. Isoprocesses: isothermal (T = const) pV = const; isobaric (p = const) V/T = const; isochoric (V = const) p/T = const. In tests identify the process first and then work with ratios: often no numbers are needed, only “by what factor does it change”.
Worked examples
Test: the temperature of an ideal gas doubles and its volume halves (mass constant). Pressure? p ∝ T/V = 2/(1/2) = 4: the pressure becomes 4 times larger.
2 g of helium (M = 4 g/mol): ν = 2/4 = 0.5 mol; number of atoms N = νN_A = 0.5·6.02·10²³ ≈ 3·10²³. Helium is monatomic, so the number of molecules equals the number of atoms.
Class activity
Chapter “map”: groups connect the ideas MKT – ideal gas – equation of state – isoprocesses with arrows on a large sheet and write one formula for each. Then groups check each other’s maps.
Practice
1
A gas in a closed vessel is being heated. Which isoprocess is this and which law applies?
Isochoric process, Charles’s law: p/T = const.
2
The gas temperature doubled and its volume tripled (mass constant). How did the pressure change?
It became 2/3 of its initial value, i.e. fell by a factor of 1.5 (p ∝ T/V = 2/3).
3
How many moles are in 88 g of carbon dioxide CO₂ (M = 44 g/mol)?
2
4
Why is gas pressure on a wall due to the impacts of many molecules and almost uniform along the wall?
The molecules are extremely numerous and move randomly, so the average impulse delivered per unit area is almost the same everywhere.